Communication systems are widely deployed to provide various types of communication such as voice, data, and so on, for a number of users. These communication systems are based on code division multiple access systems (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or Orthogonal frequency division multiple access (OFDMA).
In a typical communication system, a network is divided into a plurality of cells, such that each cell area of a cell is serviced by a base station. Specifically, a communication device located in a cell area associates with a base station servicing that cell area. The base station, then, enables the communication device to communicate with other communication devices in the communication system. The communication device can also be associated with two or more base stations at the same time. This, usually, happens when the communication device is located in an overlapping portion of the cell areas of the two or more base stations.
In an OFDMA system, a base station communicates with a communication device using a frame. The frame is divided into a downlink sub-frame and an uplink sub-frame. The base station transmits data to the communication device on the downlink sub-frame and receives data from the communication device on the uplink sub-frame.
Further, in an OFDMA mode of IEEE 802.16d/e or WiMAX, the frame comprises three segments, each with a different portion of a given frequency. In order to use a single frequency in the network, a group of adjacent base stations in the OFDMA system use different segments at high power level at different time slots for communication so as to minimize downlink and uplink interference. Thus, each base station can use one segment at a high power level and two segments at a low power level and no adjacent base stations, that share a portion of an overlapping area, use the same segment simultaneously at a high power level. A segment that is used at a high power level can service communication devices in the overlapping area of the cell area and the segments used at a low power level can service only the communication devices in a non-overlapping area of the cell area. The overlapping area can be defined as a portion of the cell area which has a possibility of overlapping with a neighboring cell area. Similarly, the non-overlapping area can be defined as a portion of the cell area which has very less possibility of overlapping with a neighboring cell area.
In existing OFDMA systems, when a communication device located in the overlapping area of a base station carries out an uplink transmission on a segment, the uplink transmission may interfere with another uplink transmission on the same segment in a non-overlapping area of a neighboring base station as the communication devices transmit at full power.
Further, for a multi-base station MBS communication, two or more base stations are required to transmit data simultaneously on the downlink transmission to a communication device in an overlapping area using the same sub channels of a segment. However, conventionally, the overlapping area is serviced by neighboring base stations using different segments at the high power level. Thus, even for communication devices in overlapping area, MBS communication cannot be facilitated by two or more base stations simultaneously, resulting in a single-base station MBS communication.
Also, the existing OFDMA systems do not facilitate macro diversity handover (MDHO). MDHO is a handover mechanism where a communication device receives same data from two or more base stations at the same time, so that the signals merge and a strong effective signal is obtained.
In addition, the existing OFDMA systems provides limited scalability as a base station can communicate with a communication device located in the overlapping area using only one segment, which is at a highest power. Thus, if the number of communication devices in the overlapping area is more than the number of regions in the segment that can be allocated, some of the communication devices may experience transmission interruptions.